Method of maintaining a laminated article under compression during a part of its manufacture

ABSTRACT

Method for magnetically clamping together selected regions of a laminated article during at least part of its manufacture, especially effective in the manufacture of magnetic cores for use in inductive devices. A predetermined magnetic field is applied to the article or established in such a way that selected regions, such as extremities which tend to flare apart, are magnetically clamped. Under certain circumstances, the magnetic field may also be used to inductively heat the selected regions of the laminated article, for example, when heat-hardenable bonding material in unhardened form is disposed between adjacent laminations in the vicinity of the regions for hardening the bonding material.

United States Patent Sims [451 June 20, 1972 METHOD OF MAINTAINING Ai561 References Clted LAMINATED ARTICLE UNDER PATENTS 0R DPlliCKnoNsCOMPRESSION DURING A PART OF 240,450 11/1911 Germany .335/294 ITSMANUFACTURE Primary ExaminerRobert L. Spicer, .Ir. Inventor. Marlon W.S'II'IS, Fort Wayne, lnd. AloM-John M. Stoudt, M E. [73] Assignee:General Electric Company Krisher, Jr., Oscar B. Waddell, Joseph B.Forman and Frank L. Neuhauser [22] Filed: July 2, 1970 57 ABSTRACT [21]Appl. No.: 51,759 I 1 Method for magnetically clamping together selectedregions Related US. Application Data of a laminated article during atleast part of its manufacture,

all fi'ecti the uf tu t m tic f [6 m is qqp is t NafiQ-Qt m- 2 LQQQLEQ;fi'f. will: Elm A Tred emu 'n ed ifimufiiifi 7 9 applied to the articleor established in such a way that selected regions, such as extremitieswhich tend to flare apart, are mag- [52] U.S. Cl ..29/602 neticallyclamped. Under certain circumstances, the magnetic [51 Int. Cl. ..B29l5/00, l-[Olf 7/06, B25b 1 H00 field may also be used to inductively heatthe selected regions [58] Field olSearch.................269/8; 29/559,602; 335/289, of the laminated wide, for p When heablwdenable bondingmaterial in unhardened form is disposed between adjacent laminations inthe vicinity of the regions for hardening the bonding material.

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METHOD OF MAINTAINING A LAMINATED ARTICLE UNDER COMPRESSION DURING APART OF ITS MANUFACTURE CROSS-REFERENCE TO RELATED APPLICATION This is adivision of my co-pending U. S. application Ser. No. 802,934 filed Feb.27, 1969 which issued as U.S. Pat. No. 3,616,056 on Oct. 26, I971.

BACKGROUND OF THE INVENTION This invention relates to improved methodsfor maintaining certain regions of the article under compression duringits manufacture when it is formed of magnetic laminations. Inparticular, the invention pertains to such improved methods especiallyeffective in the manufacture of laminated magnetic cores for use ininductive devices.

In the manufacture of a laminated article and especially laminated coresfabricated from a stack of larninations stamped out of magnetic sheetmaterial, a common and troublesome problem results from laminationdeformation or distortion. In studying the problem, I have determinedthat one cause of distortion originates from the punching operationwhich has a tendency to produce a slight elongation and deformation ofthe cut edges of the lamination, as well as sharp burrs. Another sourcemay be due to the complex configuration of the lamination which mayinclude structurally weak sections, for instance, the long and narrowtooth sections of a stator core.

Taking the laminated stator core by way of illustration, the laminationdistortions have a tendency to spread at least the outer laminations inthe stack, particularly at the tooth sections near their extremities.Such distortions in turn adversely affect the quality of themanufactured core and may be of sufficient magnitude to prevent themanufacture of a satisfactory product.

SUMMARY OF THE INVENTION It is therefore an object of the invention toprovide improved methods for maintaining under compression certainregions of a laminated article formed of magnetic material during atleast a part of its manufacture.

It is another object of the invention to provide improved methods whichovercome at least some of the difficulties mentioned above, arerelatively inexpensive to practice, and yet produce improved results inan effective and efiicient manner.

It is another object of the present invention to provide an improvedprocess for inductively heating an article during a part of itsmanufacture where preselected regions hereof have been drawn together bya magnetic field.

It is yet another object to provide an improved method of magneticallycompressing preselected regions of an article of manufacture and toinductively heat those regions.

In carrying out the objects in one form, I provide improved methods formaintaining certain regions of a laminated article of manufacture, forinstance a laminated magnetic core formed of magnetic elements, undercompression during at least a part of its manufacture For instance, inconnection with the manufacture of an unbonded dynamoelectric machinestator core, a magnetic field may be established by an electromagneticdevice, such that magnetic clamping is achieved which is particularlyeffective in compressing together or holding certain extremities orperipheral regions (e.g., tooth sections) of adjacent laminations firmlytogether.

To achieve the magnetic clamping action, the electromagnetic device andthe magnetic elements are positioned in a predetermined adjacentrelation, and the elements are magnetically clamped together byenergizing the electromagnetic device which produces the desiredmagnetic field of sutficient intensity to hold the elements undercompression in stacked relation.

This holding action reduces the size of openings which might otherwiseexist between adjacent laminations at such extremities and decreases thetendency of the core to lose heat at those locations for thoseapplications where the rate of heat loss is important.

By proper construction it is also possible to employ the sameelectromagnetic device which produces the magnetic field to heat, byinduction, the selected regions of the laminated article for one reasonor another, e.g., to harden interlaminate bonding material when thelaminated article includes such material.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. My invention itself, however, both as to its organizationand method of operation, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view, in perspective, ofapparatus which is capable of practicing one form of the inventivemethod as applied to the formation of a protective coating on selected,exposed surfaces of a laminated dynamoelectric machine stator core, thearticle of manufacture in the illustrated exemplification, the viewshowing the apparatus before the protective coating has been formed;

FIG. 2 is a horizontal cross-sectional view of certain principal partsof the apparatus shown in FIG. 1, revealing the way in which the coatingis formed in a coating-forming station on certain exposed surfaces ofthe laminated core in the exemplification,

FIG. 3 is an enlarged fragmentary view, partly in schematic form,showing the type of flux and force interaction which occurs between apart of the electromagnetic device of the apparatus shown in FIG. 2 andthe laminated core of the exemplification, when the electromagneticdevice creates a magnetic field in the vicinity of the core;

FIG. 4 is a fragmentary view, in perspective, of a portion of thelaminated core coated in accordance with the improved apparatus andmethod illustrated in FIGS. I and 2;

FIG. 5 is a cross-sectional view of an arrangement partially inschematic form, for heating the core of the exemplification prior toformation of the desired coating on selected portions of the core, withpart of the arrangement being used during the subsequent coatingformation;

FIG. 6 is a partial cross-sectional view of a modified form of thearrangement shown in FIG. 5;

FIG. 7 is a schematic circuit diagram of the apparatus of FIG. 6;

FIG. 8 is a view, in perspective, of a modified form of theelectromagnetic device, illustrated in FIGS. I3 inclusive, which may beemployed in the practice of the inventive methods;

FIG. 9 is a cross-sectional view, partially broken away, of the modifiedelectromagnetic device shown in FIG. 8, with the core of theexemplification being maintained in the coating station;

FIG. I0 is an enlarged fragmentary view, partially in schematic form, ofthe electromagnetic device and laminated core shown in FIG. 9 to revealthe type of flux and force interaction which occurs between the deviceand core when the device of this embodiment is excited;

FIG. 11 is an enlarged fragmentary view of a part of the coreillustrated in FIG. 9 to show details of the protective coating formedthereon;

FIG. 12 is an end view of another modified form of apparatus which maybe utilized in the practice of the inventive methods in connection withthe stator core of the exemplification; and

FIG. 13 is a cross-sectional view of one magnetic pole of theelectromagnetic device shown in FIG. 12, the view being taken along line13-13 in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For the purpose of disclosingcertain principles of the invention, FIGS. 1-4 illustrate one form ofthe invention in connection with the manufacture of a laminated articlein the form of 5 a stator core 10. As shown, the core is of the unbondedtype having the configuration more fully revealed in the U.S. patent ofA. A. Brammerlo, U.S. Pat. No. 3,235,762, issued Feb. I5, 1966.

Core comprises a stack of superimposed, identical laminations l2 stampedout of magnetic material, such as common electrical grade iron, into adesired configuration. Core 10 includes an annular yoke section 14 andangularly spaced apart tooth sections 16 which define coil-accommodatingpassageways in the form of slots 18. The tooth sections terminate attheir free ends in enlarged lips 20, which together form an axial bore22 adapted to receive a rotor (not shown). Opposed entrance surfaces 24and 26 of adjacent tooth section lips define restricted slot entrancescommunicating between the bore and slots in the usual way.

FIG. 4 illustrates a section of core 10 having the protective integralinsulating coating 28 already formed thereon. Note that the coating isformed on the outer surfaces of outer laminations 30 and 32 and theinterior of the slots 18. However, the bore faces 34 and slot edges 36of the tooth sections I6 are essentially free of integral insulatingmaterial.

Integrally insulated cores in which the slots and outer surfaces areinsulated by a continuous film offer cost and performance advantages.However, making a good integrally insulated core, especially of theunbonded type, requires that the core laminations be held tightlytogether. Conventionally, laminations in such cores have been heldtogether in stacked relation by welds or other mechanical securingarrangements like metal keys forced into the slots 40 formed in the yokeI4 of core 10. Even though it is desirable to clamp the outside or yokeof the core to compress the laminations in stacked relation clampingthis area offers little support to the slender and mechanically weaktooth sections 16. Consequently, there is a tendency for the laminationteeth to flare at their tips, as illustrated in FIG. 3. The flaringgenerally occurs in the outer laminations of the tooth sections, such asthe outer lamination 30a of FIG. 3. Other laminations may also exhibitsome flar- Even though the tips of the tooth sections could be held inplace by mechanical clamps, any physical contact of a clamping fixturewith the tooth laminations might interfere with the application of theintegral insulation, for example by the powder-spraying apparatusillustrated in FIGS. 1 and 2. This problem is solved in the presentinvention by applying a magnetic field to the core in such a way thatthe ends of the tooth sections are drawn or otherwise held firmlytogether during the application of a powder which forms the integralinsulation, thereby tending to eliminate the irregularities in theinsulation which occurred in the prior art due to the flaring of thetips of the tooth sections, especially were the laminations not coated,for example, with shellac.

Magnetic clamping of the laminations is particularly advantageous whenthe integral insulation is formed by the application to the cores of amaterial, such as a powdered resin, containing magnetic particles, suchas 2 per cent of a magnetic oxide pigment. The use of magnetic particlesin the material which forms the integral insulation is fully describedand claimed in Avila U.S. Pat. No. 3,l36,650. As explained in thatpatent, the application to the core of a magnetic field, after the resinapplied to the core has melted or fused, causes an increased thicknessof the coating to occur at the edges of the slots, such as edges a, band c, illustrated in FIG. 4. Prior to the Avila invention, surfacetension caused the coating to pull away from the slot edges so that thecoating on the edges was thinner than on the other areas of the corewhen it is desirable to have on the edges a coating thickness at leastas great as the thickness of the coating on other surfaces because ofthe increased wear at these edges. Of course, the magnetic field can becontrolled so that the coating material builds up on the edges to acontrolled thickness, slightly less than, the same as, or greater thanthat formed on the flat surfaces of the core, the thickness beinggreater by this approach than would otherwise occur along the edges.

FIGS. 1 and 2 illustrate a preferred embodiment of particularlyeflective apparatus capable of practicing one form of the method. Theapparatus has an electromagnetic device for magnetically clamping thetips of the tooth sections of a preheated laminated core 10, while aprotective integral insulation coating is being applied to the core bymeans of powderspraying noules. FIG. 1 illustrates core 10 at station Awhere the core is loaded into the assembly 44, and FIG. 2 illustratesthe core at station 8 where the coating-forming material is applied tothe core.

The general organization of the apparatus is illustrated in FIG. 1 andincludes a housing 42 mounted on a platform 43. The core 10 is adaptedto be mounted within a doughnutshaped electromagnetic clamping assemblyor device 44. As illustrated in FIG. 2, the electromagnetic clampingassembly 44 includes an annular iron yoke 46 enclosing two annular polepieces 48 and 50. As indicated by the dotted line 52, the pole piece 48is movable to the left to permit assembly 44 to be opened when a core 10is to be inserted therein. The pole pieces enclose an annular winding 58which together with the pole pieces produces the magnetic field used forclamping of the laminations at the tips of tooth sections 16, and forother functions, as will be described in more detail below.

Core 10 is inserted in the electromagnetic assembly 44 by opening theassembly and aligning the slots 40 with sets of lugs 60 and 62 fixed topole pieces 48 and 50, respectively. After the core is inserted inassembly 44, it is rotated until the lugs and slots 40 are no longer inalignment, and the assembly is then closed by energizing coil 58 so thatthe lugs apply mechanical clamping pressure to the yoke or outerperipheral edges of the laminations 12 forming the core 10. A powderdeflector 64 is then inserted in each side of assembly 44 by aligningpins 66 fixed to the assembly with corresponding apertures 68 formed inthe deflector 64. The pins 66 also fu nction to space the core 10 fromthe pole pieces 48 and 50 to minimize the flow of heat from thepreheated core to the iron mass of the electromagnetic elements 46, 48,and 50.

Deflector 64 also contains recesses 70 corresponding to the lugs 60,whereby the deflector may be inserted sufficiently far into the assemblyso that it functions to prevent insulation powder from entering thespace between the outer diameter of core 10 and the inside diameter ofpole pieces 48 and 50. The magnet is closed by energizing the coil 58 sothat pole pieces 48 and 50 are brought firmly together. The coil issuitably energized by applying DC or AC voltage across the leads 70which are connected to coil 58. The electromagnetic assembly 44 isgrounded by connecting a ground lead 72 to a suitable ground.

The illustrated coating apparatus also includes a suitable arrangementfor applying the protective coating material in powder form. By way ofexample the apparatus includes a pair of slewing rings 74 and 76 uponwhich are mounted four spray nozzles 78, 80, 82 and 84 having the samegeneral construction more fully disclosed in U.S. Pat. Nos. 3,355,309and 3,355,3 l0. In general, however, each nozzle is connected via a pairof hoses to a source of compressed air and also to a source of powderedmaterial, such as thermosetting epoxy resin, which may contain magneticparticles, and which will form an adherent, protective integralinsulating layer on preselected surfaces of the core which have beenpreheated to a predetermined temperature. Generally speaking, such amaterial melts, flows slightly, and coalesces or fuses onto the coresurfaces with the proper adhesion in the temperature range of I90 and232 C. As illustrated in FIG. 1, a nozzle has a hose 86 connected to asource of compressed air and a hose 88 connected to a source ofcoating-forming powder. Excess powder is recovered by means of a vacuumapplied to a hose 90 which returns the powder to the powder source.

The assembly 44 containing the preheated core is mounted on a dolly 92which moves from station A along a pair of tracks 94 to station Bbetween the slewing rings 74 and 76. The dolly and assembly pass througha rectangular opening 96 formed in the housing 42.

Once the preheated core 10 is properly positioned between the slewingrings 74 and 76, as best illustrated in FIG. 2, coil 58 is suitablyenergized, for example, by direct current or alternating current tocause magnetic flux to flow through the core laminations 12 in such amanner that the tips of the tooth sections are compressed. The coil isenergized by causing the current to flow through the leads 70 which areelectrically connected in series with the coil 58. While the coil 58 isenergized to clamp the laminations together, fusible insulating powderis sprayed by nozzles 78-84 through the slots 18 and upon the faces ofthe outer laminations 30 and 32. During each powderapplying cycle, thenozzles are rotated approximately 195 in one direction and thenapproximately 195 in the opposite direction. This oscillatory motionproduces a more uniform coating on the core than is available withapparatus in which rotation is in one direction, because the oscillatoryrotation permits the powder to impinge upon the core surfaces from twodifferent directions. Furthermore, in the illustrated embodiment, theoscillatory motion prevents the hoses attached to the nozzles frombecoming entangled with each other.

The oscillatory rotation is illustrated as being produced by areversible electric motor 96 mounted on bed 44, but the rotation couldalso be produced by a unidirectional motor coupled to a motion converterwhose output is oscillatory. Motor 96 rotates a shaft 98, to which isfixed two pulleys, each of which drives one of the slewing rings througha corresponding notched belt. The pulley for driving ring 74 is notshown in the drawings, However, slewing ring 76 is driven by means of anotched belt [00 which passes along a pulley 102 and a notched ring 104fixed to the slewing ring 76. A notched belt I06 drives slewing ring 74in a similar manner. Slewing ring 74 is rotatably mounted in a fixedframe 75 by ball bearings 77, and ring 76 is similarly mounted in afixed frame 79.

As will be discussed in more detail below, the powder may also containmagnetic particles in which case the coil 58 is energized by directcurrent so that the same magnetic field which clamps the laminationstogether will also draw the magnetic particles together with the meltedresin to the edges 0, b, and c of the core, thereby forming an increasedthickness of an integral insulating coating along these edges than wouldotherwise occur. Even though it is to be understood that the magneticclamping feature of the invention may be used during the manufacture ofarticles other than in connection with the application of fusibleresinous powder having magnetic particles, in the following discussionof the preferred embodiment as illustrated in FIGS. 1 and 2, it will beassumed that the integral insulation is formed by the application of apowdered, fusible resin containing particles of magnetic oxide of thetype dis closed in the Avila U.S. Pat. No. 3,136,650.

Before the electromagnetic assembly 44 is positioned between the slewingrings 74 and 76, a mask assembly 38 may be inserted in the bore 22 ofthe core 10. One type of such assembly is more fully disclosed in theabove mentioned U.S, Pat. No. 3,355,309. However, it is partiallyillustrated in FIG. 2. Generally, the mask consists of an inlet 108, acavity 110 and a plurality of projections H2, The outer surface of thecavity engages the inside of the bore 22 and the projections projectinto the entrances 18 just beyond the flared tips of the tooth sections16 to prevent coating material build-up in the entrances and bore 22.

The magnetic field configuration generated by the electromagnet isillustrated in FIG. 4 relative to the pole piece 50 and the upperright-hand portion of core 10, as viewed in FIG. 2. The magnetic linesof flux are indicated by the dashed lines 114 in FIGS. 2 and 3.

One may think of magnetic forces on a piece of iron in air as arisingfrom the entry of flux lines into, and the exit of flux lines out of,its surfaces. For practical purposes, it is believed correct to considerall flux lines as entering and emerging from the iron at right angles toits surface. Qualitatively, the phenomenon is as if the flux linesemanating from the iron were like rubber bands in tension. Linesentering or leaving the upper surface pull the iron up whereas linesentering or lowering a lower surface pull it down. The net force on apiece of iron in a magnetic field is the resultant of all the tensionson all its surfaces.

Ouantitatively, the forces depend upon flux density at the surface. Foriron surrounded by air, the "tensile pressure" on the surface is givenby F= 1.391310' pounds per square inch, where B is the flux density atthe region in question in lines per square inch.

One method of obtaining the proper magnetic clamping force is to createa condition in which the number of flux lines crossing the toothlamination surface facing the center of a tooth section is greater thanthat crossing the opposite surface. Such a field configuration willproduce a net force which will pull the lamination toward the center ofthe stack. In an ideal field configuration, all the flux would enter atthe edges of laminations (thereby producing neither flaring nortightening forces), and leave from the surface at the center of a toothsection.

Another method of obtaining the desired magnetic clamping force is todirect the flux lines through a lamination so that the points of entryand exit of at least some lines are offset, i.e., the entry and exitpoints on the parallel surfaces of the lamination are not directlyopposite each other. Such a field configuration produces a magneticmoment which forces the tooth tip portion of the lamination towards thecenter of the stack of laminations while producing a force which tendsto flare the yoke portion of the lamination away from the stack, Themagnetic clamping assembly 44, as illustrated in FIGS. 1, 2, and 3,produces a magnetic field configuration which employs both of thesemethods to obtain the desired magnetic force to clamp together the tipsof the tooth sections of the core.

As illustrated in FIG. 3, the majority of the flux lines emanate frompole piece 50, enter the edges of the lamina tions 12 in a directionsubstantially parallel to the plane of the laminations, travel throughthe laminations toward the center of the tooth section, and then leaveeach lamination in a direction which is substantially perpendicular tothe plane of the lamination whereby there is developed a resultant magnetic force tending to force the tip of lamination 30a to the lefi,thereby eliminating flaring of the lamination. Consequently, the toothtips of all the laminations tend to be drawn to the center of the toothsection, that is, to the left in FIG. 3, thereby compressing thelaminations to eliminate flaring. In other words, all of the flux whichenters each lamination must exit in a direction substantiallyperpendicular to the left-hand surface of the lamination thereby causinga resultant moment which favors drawing the tip or lower portion of thelamination to the left. It is believed that the resultant favorablemoment occurs due to a large number of flux lines that enter the edgesof the laminations substantially parallel to the planes of thelaminations but leave the laminations substantially perpendicularthereto. Due to the high flux density at the yoke end of lamination 30a,together with the shunting effect of the next adjacent lamination 30b,there is also a magnetic force which tends to pull the yoke end oflamination 30a to the right, that is, tends to flare the yoke end oflamination 300. This flaring tendency can be quite high at large valuesof magnetic field intensity, but the lugs 60 and 62 fixed to the polepieces of the electromagnet firmly clamp the yoke portion of the core sothat flaring does not actually occur.

In an actual use of the invention, coil 58 had 350 turns, and the powersource connected to the coil produced magnetic fields of up to 17,000ampere turns. However, the intensity of the field required to pull thetooth tips together depends on how badly they are flared, the dimensionsof the core, and the distance between the core and electromagneticdevice, among the more important factors. Furthermore, the fieldrequired for holding the laminations together is less than that requiredfor initially overcoming the flaring.

When magnetic oxide particles are included in the powder applied to thepreheated core 10, the same unidirectional or DC magnetic field whichprovides the clamping of the tips of the tooth sections also draws theintegral insulation-forming material toward the edges a, b, and c, asillustrated in FIG. 4, thereby causing an increased thickness ofintegral insulation to form along those edges than would otherwise bethe situation. This magnetic drawing is accomplished by maintaining theelectromagnet energized for a short time after the powder is applied tothe core. It has been found that the application of the magnetic fieldduring the spraying of the powder upon the core does not adverselyaffect the pattern of distribution of the powder; i.e., the powder issubstantially uniformly distributed along the surfaces of the coreslots. After the coating material has set or cured, for example, byfurther heating of a thermosetting material, the electromagnet isdeenergized to remove the magnetic field, and the cured material whichis now bonded to the lamination, will mechanically hold the laminationstogether.

FIG. illustrates a variation of the embodiment illustrated in FIGS. 1and 2, whereby an electromagnet device 115 can be used not only tomagnetically clamp the core laminations and to draw an insulatingcoating containing magnetic particles toward the slot edges in order toprovide an increased thickness of integral insulation about those edges,but also to inductively heat the core 10 both prior to thepowder-spraying operation and also after the magnetic drawing operation,if such is desired. In FIG. 5, a T-shaped magnetic member 116 ispositioned such that one leg 118 contacts the pole piece 48 of magnet11S and another leg 120 extends completely through the bore 22 of core10. Another magnetic member 122 is placed in contact with the pole piece50 and with the leg 120. The magnetic members 116 and 120 are clamped inposition by suitable clamps 124 and suitable fastening means such as thethreaded fastener 126. The bore and slot edge masking assembly 38 is notused in the embodiment illustrated in FIG. 5. The magnetic elements 116and 122 form closed magnetic paths with the electromagnet 115. Thesemagnetic members, together with the electromagnet and core 10 define atransformer arrangement in which the coil 58 forms the primary windingof the transformer and the core 10 effectively forms a single turnshort-circuited secondary winding. Coil S8 is electrically connected vialeads 70 to a double pole, double throw switch 128. The switch may beoperated to connect the coil either to a suitable source, such as an ACpower source 130, to establish a varying magnetic field for inductiveheating purposes or to a suitable source, such as a DC power source 132,to establish a unidirectional magnetic field.

Just prior to the loading of the electromagnet 115 containing core 10into the spraying apparatus, i.e., at station A, switch 128 is placed inthe condition illustrated in FIG. 5 to apply AC power to coil 58. Theresulting AC current, for example 30 amperes at 140 Hertz establishes avarying magnetic field which inductively heats core 10 to place it inthe preheated condition previously referred to. The resultant magneticfield produced by coil 58 also produces the magnetic tightening effectat the tips of the core tooth sections as previously described. When thecore is preheated to the temperature at which the insulating powder willfuse and adhere to the core laminations, the powder is applied to thecore. When the powder has melted, the switch 128 is operated to itsother position to connect the DC power source 132 to the coil 58. Themagnetic field resulting from the direct current flowing in coil 58maintains the magnetic clamping effect at the tips of the tube sectionsand also draws the magnetic oxide-containing resin, which is now in aliquid state, toward the slot edges to provide an increased thickness ofinsulation coating thereon. After the coating has built up to asufficient thickness along the slot edges (a matter of a few seconds)switch 128 is returned to the position illustrated in FIG. 5 so that ACpower is applied to coil 58, thereby resulting again in inductiveheating of core 10. The switch 128 is maintained in this position untilthe core has been heated to a sufficiently high temperature for asufiiciently long period of time to cure or set the magneticoxide-containing resin, thereby bonding the magnetic oxide resin to thecore to fonn an integral insulation on the core. Once the resin has set,the laminations are tightly bonded together by the coating, andtherefore the core 10 may be removed from the fixture and thelaminations will be held tightly together by the integral insulation asillustrated in FIG. 11.

FIGS. 6 and 7 illustrate another embodiment of the invention in whichthe core may be heated simultaneously while the laminations thereof aremagnetically compressed.

The embodiment of FIG. 6 utilizes the same transformer action utilizedin the embodiment of FIG. 5. However, the leg of magnetic element 116extends only as far as the line 133, and the magnetic element 122includes a horizontal extension which is adapted to abut the leg 120 andwhich also provides the core upon which to wind an annular coil 13B Leg120 also carries an annular coil 134 and a bore coil 136. The functionof these various coils will be described in connection with the circuitdiagram of FIG. 7. When it is desired to inductively heat andmagnetically clamp the core laminations together, a switch 142 is in theposition illustrated in FIG. 7 and connects coils 136, 134 and 138 inseries across a source of AC power. In this embodiment, the coil 58contains 323 turns instead of 350 turns used in the previous embodimentsand is not used in the inductive heating step. When the core has reachedthe temperature suitable for the application of the magneticoxide-containing resin powder, switch 142 is moved to its alternateposition to connect coils 136 and 58 in series across a DC power supplyto maintain the laminations magnetically compressed and also to draw themagnetic resin to the slot edges of the core to assure that a protectivecoating of sufficient thickness is formed at these edges. In order toobtain a greater inductive heating effect, the circuits of FIG. 7 couldbe modified so that coil 58 is also energized by the AC power during theheating step.

FIGS. 8-10 illustrate another embodiment of the invention which reducesthe tendency of the laminations to flare along the yoke of core 10. Inthis embodiment, an electromagnetic device 144 is inserted in the bore22 of core 10. The device consists of an annular coil 146 wound on amagnetic core 148. Coil 146 is adapted to be connected via lead 149 tothe same DC source which energizes the coil 58. The magnetic field 152generated by coil I46 produces a force which opposes the force producedby the field from coil 58. Even though the resultant force is in adirection that would tend to flare the tips of the teeth along the bore22, this force is not great enough to cause the tips of the toothsections to flare. In effect, the center of the magnetic force is movedto the center of the lamination, and the stiffness of the lamination issufficient to keep the ends of the lamination from flaring up.Consequently, the addition of the electromagnetic device 144 produces aresultant clamping force which is more uniformly distributed over thelamination surface while eliminating flar ing at both the yoke and toothtips.

FIG. 11 illustrates the manner in which the integral insulating coating28 covers the edges of the slot with an increased thickness of coatingand also fills in small spaces, if any, that might exist between thelaminations of the core along the slot walls.

FIGS. 12 and 13 illustrate another embodiment of the invention. Fourelectromagnetic assemblies 154, 156, 158, and are mounted in a frame162. As illustrated in FIG. 13, each electromagnetic assembly, such asassembly 154, consists of a coil 164 wound on the legs of a U-shapedmagnetic core 166 secured to frame 162 by means of bolts 168. Alaminated stator core 170 is positioned in the center of frame 162. Theyoke 174 of the core has four equally spaced flat portions, each ofwhich engages the ends of the legs of a different one of the U-shapedmagnetic cores. For example, the

flattened portion 172 engages the ends of the legs of the U- shaped core166 of electromagnet assembly 154. The electromagnetic device 144 isinserted in the bore of a core 170.

In operation. core 170 is preheated and placed in the frame 162. Thecoils of the electromagnetic assembly are connected in series with eachother and with the electromagnet device 144 to produce in core 170 thegeneral flux configuration as illustrated in FIG. 10 for tightening thetips of the tooth sections of the core. Furthermore, if the coatingmaterial applied to the core contains magnetic particles, the magneticfield draws the coating material towards the slot edges of the core sothat the coating builds up to a thickness which is greater than thatwhich would occur if magnetic powder and a magnetic field were not used.The arrangement illustrated in H65. 12 and 13 also reduces the flaringof the laminations at the yoke 172 of core 170. To accomplish thisresult, the cores are mounted in such a manner that some slight radialmovement is permitted so that when the magnetic coils are energized, theU-shaped cores are magnetically attracted to the yoke of core 170 tofirmly engage the yoke so that the resulting friction restricts flaringof the core laminations at the yoke.

It will be appreciated from the foregoing disclosure that the methodsand apparatus of the present invention, among other advantages, may berapidly, efficiently and easily practiced to manufacture articles ofimproved quality. Moreover, the methods are quite versatile in nature.In regard to this latter feature, the electromagnetic devices describedabove (see FIG. 7, for instance) may be quite efi'ectively employed toproduce laminated cores having interlaminate bonds. For example, withthe laminations disposed in stacked relation and adherent bondingmaterial in unhardened form between adjacent laminations, the devicesmay be excited to generate the requisite magnetic field for firmlyholding together the laminations in stacked relation until theinterlaminate bonding material has become sufficiently hardened. Wherethe inter laminate bonding material is of the thermo-responsive,heathardenable type (as compared with a pressure-sensitive material), ifdesired, the same electromagnetic devices may also be used toinductively heat the laminated stack to the proper temperature in themanner already explained to produce sufficient heat for hardening thematerial. Bonded cores having such material are more fully disclosed inthe Delean et al. US. Pat. No. 3,293,471 and the Hull US. Pat. No.3,299,304.

Thus, while in accordance with the Patent Statutes, I have describedwhat at present is considered to be the preferred embodiments of myinvention, it will be obvious to those skilled in the art that numerouschanges and modifications may be made therein without departing from theinvention, and it is therefore intended in the appended claims to coverall such equivalent variations as fall within the true spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A method of firmly holding together magnetic laminations in apreselected portion of a laminated structure comprising the steps ofgenerating a magnetic field having lines of flux; and directing thelines of flux through at least one of the laminations so that some ofthe lines enter and leave opposite parallel surfaces of the at least onelamination at points on the surfaces which are not opposite each other,thereby creating a magnetic moment which clamps at least one laminationto the remainder of the laminated structure in the preselected portion.

2. The method of fimily holding together magnetic laminations in the tipof a tooth section of a laminated stator core having an outer yokesection and inner tooth sections defining a bore, the method comprisingthe steps of generating a magnetic field having lines of flux; directingthe lines of flux through at least one of the laminations in a directionto produce resultant magnetic forces which clamp at least one of thelarninations in the tip of a tooth section to other parts of thelaminated stator core' and mechanical] clam ing together the laminationsm the yoke section as t e tip 0 the tooth section is being clamped toother parts of the laminated stator core.

3. The method as defined in claim 2 wherein a portion of the lines offlux are directed along a substantially parallel path segment and enterthe laminated stator core via the yoke section and another portion ofsaid lines of flux enter said laminated stator core via the tip of saidtooth section.

4. A method of maintaining an article having magnetic elements undercompression during a part of manufacture thereof comprising the stepsof: positioning a first electromagnetic device and the article in apredetermined adjacent relation with respect to one another, andmagnetically com pressing preselected regions of the magnetic elementstogether by energizing the first electromagnetic device and establishinga predetermined magnetic field of sufficient intensity to apply acompressive force to the magnetic elements during the manufacture of thearticle thereby drawing the preselected regions together.

5. The method of claim 4 including the step of inductively heating themagnetic elements by exciting the first electromagnetic device toproduce a magnetic field and effecting an increase in temperature of themagnetic elements.

6. The method of claim 4 in which the magnetic elements have unhardenedbonding material disposed between adjacent elements, and the methodincludes the further step of generating a magnetic field, by energizingthe first electromagnetic device, of sufficient intensity to place themagnetic elements under compression until the bonding material hardens.

7. The method of claim 6 in which the bonding material is of thethermo-responsive, heat-hardenable type and wherein the further stepincludes inductively heating the magnetic elements by exciting the firstelectromagnetic device to effect a magnetic field for increasing thetemperature of the magnetic elements thereby applying heat to thebonding material before it becomes hardened.

8. The method of claim 4 in which the article is a laminated stator corehaving a yoke section and tooth sections formed with tips defining abore and wherein positioning the first electromagnetic device andarticle includes placing the first electromagnetic device outwardly andin the vicinity of the stator core; and the method includes maintainingthe laminated stator core and the first electromagnetic device in thatposition while magnetically clamping tooth section tips together.

9. The method of claim 8 further comprising positioning a secondelectromagnetic device adjacent the bore of the laminated stator core,concurrently energizing the first and second electromagnetic devices toestablish magnetic fields, and magnetically compressing the yoke sectionand tooth section tips to draw the respective regions together.

1. A method of firmly holding together magnetic laminations in apreselected portion of a laminated structure comprising the steps ofgenerating a magnetic field having lines of flux; and directing thelines of flux through at least one of the laminations so that some ofthe lines enter and leave opposite parallel surfaces of the at least onelamination at points on the surfaces which are not opposite each other,thereby creating a magnetic moment which clamps at least one laminationto the remainder of the laminated structure in the preselected portion.2. The method of firmly holding together magnetic laminations in the tipof a tooth section of a laminated stator core having an outer yokesection and inner tooth sections defining a bore, the method comprisingthe steps of generating a magnetic field having lines of flux; directingthe lines of flux through at least one of the laminations in a directionto produce resultant magnetic forces which clamp at least one of thelaminations in the tip of a tooth section to other parts of thelaminated stator core; and mechanically clamping together thelaminations in the yoke section as the tip of the tooth section is beingclamped to other parts of the laminated stator core.
 3. The method asdefined in claim 2 wherein a portion of the lines of flux are directedalong a substantially parallel path segment and enter the laminatedstator core via the yoke section and another portion of said lines offlux enter said laminated stator core via the tip of said tooth section.4. A method of maintaining an article having magnetic elements undercompression during a part of manufacture thereof comprising the stepsof: positioning a first electromagnetic device and the article in apredetermined adjacent relation with respect to one another, andmagnetically compressing preselected regions of the magnetic elementstogether by energizing the first electromagnetic device and establishinga predetermined magnetic field of sufficient intensity to apply acompressive force to the magnetic elements during the manufacture of thearticle thereby drawing the preselected regions together.
 5. The methodof claim 4 including the step of inductively heating the magneticelements by exciting the first electromagnetic device to produce amagnetic field and effecting an increase in temperature of the magneticelements.
 6. The method of claim 4 in which the magnetic elements haveunhardened bonding material disposed between adjacent elements, and themethod includes the further step of generating a magnetic field, byenergizing the first electromagnetic device, of sufficient intensity toplace the magnetic elements under compression until the bonding materialhardens.
 7. The method of claim 6 in which the bonding material is ofthe thermo-responsive, heat-hardenable type and wherein the further stepincludes inductively heating the magnetic elements by exciting the firstelectromagnetic device to effect a magnetic field for increasing thetemperature of the magnetic elements thereby applying heat to thebonding material before it becomes hardened.
 8. The method of claim 4 inwhich the article is a laminated stator core having a yoke section andtooth sections formed with tips defining a bore and wherein positioningthe first electromagnetic device and article includes placing the firstelectromagnetic device outwardly and in the vicinity of the stator core;and the method includes maintaining the laminated stator core and thefirst electromagnetic device in that position while magneticallyclamping tooth section tips together.
 9. The method of claim 8 furthercomprising positioning a second electromagnetic device adjacent the boreof the laminated stator core, concurrently energizing the first andsecond electromagnetic devices to establish magnetic fields, andmagnetically compressing the yoke section and tooth section tips to drawthe respective regions together.